This invention relates to a method for the face-to-face weaving of a pile fabric whereby on a weaving machine in successive insertion cycles in each case two weft threads are inserted almost simultaneously between binding warp threads and pile threads, so that two backing fabrics are woven, so that pile threads have parts which form pile according to a two-shot weave and have other parts which are inwoven in a backing fabric, and so that two pile threads perform a pile change, whereby the successive positions (B=bottom; M=middle; T=top) of each pile thread are predetermined in relation to the weft threads in a series of successive lift plans, of which every lift plan determines the positions in relation to the weft threads of two successive insertion cycles.
With such a generally known method for the face-to-face weaving of a pile fabric the binding warp threads are positioned by weaving frames and the pile threads are, by means of a jacquard machine, individually positioned in relation to the levels at which both weft threads will be simultaneously inserted.
The positioning of the binding warp threads occurs such that the binding warp threads weave in weft threads at two levels and form a top and a bottom backing fabric, whereby of the two weft threads inserted in one and the same insertion cycle in each case one is inwoven in the top backing fabric and one in the bottom backing fabric.
The positioning of the pile threads occurs such that pile threads with different visible properties (such as for example their color) form pile in different areas of the pile fabric corresponding to a predetermined pattern which is to be made visible in the pile fabric. The formation of pile occurs according to a two-shot weave whereby the pile-forming pile thread is alternately passed around a weft thread of one of the backing fabrics and around a weft thread (which was inserted during the following insertion cycle) of the other backing fabric. Non-pile-forming parts of the pile threads are inwoven divided up in the top and the bottom backing fabric. For each pile thread it is predetermined in which backing fabric the non-pile-forming parts have to be inwoven. If in two pile rows two pile threads differing in color form pile one after the other in warp direction then a pile change is performed between these two pile threads.
A pile change of a first and a second pile thread implies that the situation whereby the first pile thread forms pile while the second pile thread is inwoven in a backing fabric is reversed after a well-defined insertion cycle so that from the following insertion cycle the first pile thread is inwoven and the second pile thread forms pile.
It is further also generally known that the positions which every pile thread must occupy in relation to the successively inserted weft threads can be predetermined in a series of successive lift plans. Each lift plan determines the positions of a pile thread in relation to the two pairs of weft threads which have been inserted during two successive insertion cycles. A lift plan can be a graphic or a symbolic representation of a number (in this case two) of successive positions of a pile thread, whereby for every position (per shot) there are three different possibilities, namely top, middle and bottom. For each of these three possible choices a lift plan must therefore be able to give a different indication (symbol). Generally a lift plan is to be considered as a position instruction which determines the, positions for a pile thread in relation to the weft threads which have been inserted during a number (two) of successive insertion cycles. A lift plan is therefore derived from an elementary weave over a specific weft repeat. The positions of the pile threads are determined per two insertion cycles. In order to form a pile loop two insertion cycles must indeed also be performed. The state (pile-forming or inwoven) of a pile thread therefore in each case remains the same for at least two insertion cycles.
In this specification and in the claims a lift plan of a pile thread is indicated by means of two letters placed between square brackets which respectively indicate the successive positions (B=bottom; M=middle; T=top) of this pile thread in relation to the weft threads inserted one above the other during two successive insertion cycles.
The pile threads extending between the two backing fabrics are subsequently cut through so that two pile fabrics are obtained. Each pile fabric comprises a backing fabric with weft threads inwoven by binding warp threads and a large number of pile loops, with upright pile tufts, passed around weft threads.
It is also known that a number of pile changes of pile threads with different properties, such as for example a different color, cause effects which adversely affect the quality of the fabric. Thus there are pile changes which cause mixed contours and/or double-acting pile tufts.
The purpose of a pile change of two pile threads with different visible properties (such as e.g. color) is to obtain two areas in a pile fabric with a different appearance (color) corresponding to a predetermined pattern. Such a pile change results in mixed contours if a pile tuft of one of the pile, threads is in the area where the other pile thread forms pile. Because of this the dividing line between the two areas is disrupted and a pattern is obtained with blurred contours. Such mixed contours are especially disadvantageous if it concerns a pile change of two differently colored pile threads. The disrupted dividing line between neighboring color fields causes a blurry looking pile pattern, so that an inferior pile fabric is obtained.
If two pile tufts extend between the same weft threads of a backing fabric located one next to the other and are therefore not separated from each other by an intermediate weft thread this also results in a disruption of the appearance of the pile fabric. There are also a number of pile changes which cause such a fault, which are indicated as "double-acting pile tufts."
There are also pile changes which give the result that a pile thread when forming a first pile loop around a weft thread located along the back cannot be tightly stretched. This causes an imperfect design on the back of the pile fabric.
Mixed contours can be avoided by not allowing any pile threads to form pile during a pile change for two consecutive insertion cycles. In that manner a clear separation is obtained between two areas with a different appearance. A disadvantage of this is that a pile loop must be eliminated. This is not always possible. Furthermore this must always be taken into account when drafting the card design. This causes much additional work.
Another known method for avoiding mixed contours consists in determining the positions of the various pile threads in relation to the successive weft threads in a series of successive lift plans, of which every lift plan determines the positions in relation to the weft threads which have been inserted during three successive insertion cycles. A working repeat is thus obtained for the pile threads that runs over three insertion cycles, while the working repeat for the binding warp threads (for forming the backing fabrics) runs over two insertion cycles. If lift plans are initially provided for the pile threads which determine the positions in relation the weft threads of two consecutive insertion cycles, then this method implies that all lift plans of all pile threads must be changed.
A first purpose of this invention is to provide a method for the face-to-face weaving of a pile fabric according to which certain undesirable effects which are the result of a pile change can be avoided without having to take them in account when drafting the card design. A second purpose of the invention consist in avoiding these undesired affects without having to change all provided lift plans of all pile threads for that purpose.
These objectives are attained by providing a method with the characteristics mentioned in the first paragraph of this specification, whereby according to this invention an effect that could be the result of a pile change is prevented by replacing the last lift plan of at least one of the pile threads which perform the pile change prior to the pile change and/or the first lift plan after the pile change by a correction lift plan.